The present invention relates to a method of producing a p-type ZnSe crystal having low resistivity useful as a material for a blue laser, a blue light emitting device, etc.. ZnSe has been anticipated as a material for a blue laser, a blue light emitting device and so on, since its band gap corresponds to blue luminescence. A ZnSe crystal has been produced so far by a molecular beam epitaxy (MBE) process or a metal organic vapor deposition (MOCVD) process.
According to the MBE process, a metal element Zn and a non-metallic element Se are vaporized in an atmosphere at an ultra-high degree of vacuum so as to obtain an intensity of a molecular beam corresponding to vapor pressure of each element, and a crystal is grown up while controlling an atomic layer.
On the other hand, thermal decomposition of an organometallic compound is used for production of a ZnSe crystal in the MOCVD process.
In order to obtain a p-type ZnSe crystal, it is necessary to dope ZnSe with N during crystal growth. For N doping, gaseous N.sub.2 molecules for instance are dissociated with electromagnetic wave RF, and radical N is introduced to ZnSe epitaxially growing on a substrate.
Since ZnSe is doped with sole N during crystal growth in a conventional method, acceptor concentration of N is not increased more than 10.sup.18 cm.sup.-3. Even if further addition of N to ZnSe is tried, it is impossible to increase concentration of the carrier due to the compensation mechanism; a N atom located at a substitutional position of Se transfers to an interstitial position when acceptor concentration of N exceeds 10.sup.18 cm.sup.-3 and turns to a donor (n-type), so that N atoms acting as p-type acceptors are diseffected by N atoms acting as p-type donors.